Controlling access to disseminated messages includes implementing one or
more key management policies that specify how various encryption keys are
maintained and in particular, when encryption keys are made inaccessible.
Deleting a particular key renders inaccessible all copies of messages,
known or unknown, associated with the particular key, regardless of the
location of the associated messages. A message may be directly associated
with a deleted key. For example, a message may be directly associated
with a deleted key by having been encrypted using the deleted key. A
message may also be indirectly associated with a deleted key. For
example, a message may be indirectly associated with a deleted key by
being encrypted with a key that in turn was encrypted using the deleted
key. Any number of levels are indirection are possible and either
situation makes the message unrecoverable. The approach is applicable to
any type of data in any format and the invention is not limited to any
type of data or any type of data format. Examples of data include, but
are not limited to, text data, voice data, graphics data and email.
Although embodiments of the invention are described hereinafter in the
context of controlling access to email, the invention is not limited to
the email context and is applicable to controlling access to any type of
messages or data.